1. Field of the Invention
The present invention relates to apparatus and method for facilitating installation of optical-fiber (fiber optic) cable used for communication purposes and, more particularly, for mechanically splicing optical-fiber cable in the field during installation in a manner that results in an efficient optical interface without producing harmful light reflections.
2. Description of Prior Art
The evolution of communication technology is in the direction of ever-faster communication with ever-increasing bandwidth. Optical-fiber cable offers these improvements over copper wire, but imposes challenges which copper wire technology did not present. For example, copper wires can be readily spliced and/or soldered together, where the resultant contact or joint almost always offers good electrical conductivity without inhibiting communication, but not so with optical-fiber cable. Optical-fiber cable (also known as fiber-optic cable), made from glass, is not capable of being readily spliced in a time-efficient manner, as compared with copper wire splices. Optical-fiber uses light energy as its communication medium rather than the familiar flow of electrons, i.e., “electricity”, used in copper wire. A bad optical “joint” can attenuate forward light transmission and cause reflection of light waves back to the light source which can interfere with operation of the light source and become a major problem.
The assignee of the present invention is a large telecommunications company which is installing optical-fiber cable (fiber optics) to its present and future customer base. When installing this fiber into apartment houses or multiple dwelling units (MDU's), the current technique is to bring the optical-fiber cable from, for example, a pole on the street to an external terminal affixed to the outside of the MDU building. From that connection point, a path is created to each apartment unit by using “microduct” which is a protective casing which may have an inside diameter of approximately 0.25-0.50 inches. A fiber optic cable which may have an outside diameter of approximately 0.125 inches containing a clad optical strand along the longitudinal axis of the cable is pulled through the microduct into each dwelling unit. For a two-hundred unit apartment building, for example, two-hundred separate microducts each containing its own optical cable with centralized and clad glass optical strand is connected from the external terminal, each microduct going to one of the two-hundred apartments respectively.
Today, fiber optic cable of pre-determined lengths with factory-connectorized both ends can be readily obtained. The connectors of these connectorized ends then can readily plug into jacks which are designed to matingly-accept the connectors. Although this would eliminate the need for splicing optical-fiber cable in the field, a connector is too large to fit into and through the microduct. The cross-sectional dimension of these connectors can be at least an order of magnitude larger than the outside diameter of the fiber optic cable for which they act as terminations. Larger diameter microduct could be used to accommodate pre-connectorized optical-fiber cable, but with a large apartment building (e.g., 200 units) a space issue develops—there simply isn't enough space to bundle 200 “large-diametered” microducts and run them up a wall inside a building prior to their being dispersed to the 200 dwelling units. That would require too much space. Thus, the small inside diameter microduct is used which requires elimination of one pre-connectorized end. Indeed, each un-connectorized or “raw” glass fiber end is fed through the microduct into one of the dwelling units. That raw end then needs to be properly and optically coupled to something that would serve to continue the light energy communication to its intended destination. There could be an optical coupling to a raw glass end of another optical cable in an apartment, the other end of the other optical cable being pre-connectorized and connectable to a wall plate, or the equivalent, mounted in the apartment. In other words, an optical cable splice of the two “raw” optical-fiber ends needs to be performed in the apartment unit.
The current method of making such a splice involves melting the ends of the glass strands where they touch in what is called a “fusion” splice. This may be analogous to welding two pieces of metal together. The glass strands are only microns in diameter, possibly on the order of 100 microns or less. (One micron is one-thousandth of a millimeter or about 0.000039 inch.) In the fusion splice, the strands are cut at right angles to the axis of the strand. The fusion splice, involving an electrical arc, is sufficiently good to avoid both substantial forward transmission light-loss and substantial problematical light reflection, the latter of which otherwise could be reflected back to the light source causing serious problems. However, a major drawback in performing the fusion splice is the very long time required for a technician to perform the splice—some 45 minutes or longer per splice. When outfitting a 200 unit apartment building, for example, this can result in a large man-hour impact, negatively impacting the costs of installation.
What is needed is a technique for providing a splice between two glass strand ends of mere microns in diameter, each contained within its own optical-fiber cable, in a quick and efficient manner as compared with the present forty-five minute splice-time needed for a fusion splice, and which provides a splice that (1) does not significantly attenuate forward transmission of the light signal and (2) does not return light reflections from the splice via the optical-fiber back to the light source, otherwise causing damage or deteriorated operation. The present invention is a welcome solution to these drawbacks of the prior art.